In the related art, an Oxygenator which performs gas exchange using a hollow fiber membrane layer constituted with a plurality of hollow fiber membranes is known (for example, see U.S. Pat. No. 6,503,451).
The Oxygenator described in U.S. Pat. No. 6,503,451 has a housing, hollow fiber membrane layers which are housed in the housing and form a cylindrical shape as a whole, a blood inlet, a blood outlet, a gas inlet, and a gas outlet. In the Oxygenator, through each hollow fiber membrane, gas exchange between blood and gas, (i.e., a process of adding oxygen and removing carbon dioxide) occurs.
In the hollow fiber membrane layers having a shape of a cylindrical body, a plurality of hollow fiber membranes are integrated and laminated on one another. In each of the layers, hollow fiber membranes are wound one by one around the central axis of the cylindrical body, and in this state, the hollow fiber membranes travel between a partition at one end of the cylindrical body and a partition at the other end of the cylindrical body. In an outward path heading for the partition at the other end from the partition at one end, each hollow fiber membrane is wound at least once around the central axis of the cylindrical body. Moreover, in a homeward path heading for the partition at one end from the partition at the other end, each hollow fiber membrane is also wound at least once around the central axis of the cylindrical body.
In each of the hollow fiber membranes wound as above, a length of the layer wound once around the central axis of the cylindrical body increases toward the outer circumference of the cylindrical hollow fiber membrane layer. The Oxygenator has a problem in that the larger the length of the hollow fiber membrane from one partition to the other partition is, the greater the pressure loss of gas passing through the inside of the hollow fiber membrane becomes.